Furnace for wave soldering of tin is one of important facility for an electrical factory. The furnace for wave soldering of tin is a high energy consumption facility, especially for the preheat section. In prior art, the preheat section generally comprised two or three preheat zones, each of which had a width of 60 to 80 cm. An electrical controlled system was introduced to control heating power of a heater according to a set temperature, to ensure that a PCB (Printed Circuit Board) was heated to a best temperature for the wave soldering after passing through the preheat section. The preheat section had an energy consumption of about 30 to 45 kW, generally accounting for 60% to 70% of the total energy consumption of the furnace.
Although the PCBs are in variable sizes, all tubes of the heaters must be opened because of the designed structure of the tubes, and this causes waste of electrical energy for unused parts of the tubes, when preheating the PCBs with relative small sizes.
FIG. 1 illustrates a schematic diagram of the preheat section in the furnace for wave soldering of tin in the prior art. Referring to FIG. 1, the preheat section 10 in the furnace for wave soldering of tin comprised three preheat zones 101, 102, and 103, which are set parallel in a plane. A guider 106 is set above the preheat zones 101, 102, and 103. A PCB 104 is transferred from the preheat zone 101 to the preheat zone 102 and 103 along the guider 106 (directed by an arrow as shown in FIG. 1). Each one of the preheat zones 101, 102, and 103 comprises a plurality of heating tubes 104, which are set parallel, and the axial direction of the heating tubes 105 is perpendicular to the moving direction of the PCB 104.
As illustrated in FIG. 1, the preheat zones 101, 102, and 103 had length of 700 mm, and width of 600 mm. The axial direction of the heating tubes 105 is perpendicular to the moving direction of the PCB 104, in other words, the axial direction of the heating tubes 105 is the breadth direction of the preheat zones 101, 102, and 103. Furthermore, the length of each of the heating tubes 105 is substantially equaled to the width of the preheat zones 101, 102, and 103. If the PCB 104 had a small size, for example 200 mm in the length and 150 mm in the width, when the PCB 104 moved along the direction perpendicular to the axial direction of the heating tubes 105 through the preheat zones 101, 102 and 103 in sequence, only a part with 150 mm in length of each heating tube 105 was useful for the PCB 104. But all the heating tubes 105 must be opened as a whole when preheating the PCB 104. So it caused the waste of electrical energy for the opened part uncovered by the PCB 104 in the axial direction of the heating tubes 105, as the part defined by a dash line frame illustrated in FIG. 1, which were opened but no contribution to the PCB 104.
The size of the preheat zone is 700 mm*600 mm, and each preheat zone contains 6 heating tubes 105 with 600 mm in length and 2 kW in energy consumption, so the power of each preheat zone is 12 kW, and the total power of the three preheat zone is 36 kW. The energy consumption of the preheat zone is not influenced by the size of the PCB 104 for all the heating tubes 105 must be opened. In other words, the total heating power is always 36 kW, whatever the size of the PCB 104 is large or small.
So a new heating structure muse be designed to reduce the waste of power and conserve energy.